PROJECT SUMMARY Our studies on the biology of survivin, and its contribution to tumor progression in humans, have reached important milestones during the last cycle of CA78810. We now know that the anti-apoptotic function of survivin involves a pool of the molecule compartmentalized in mitochondria, and released in the cytosol in response to cell death stimuli. We also know that mitochondria-derived survivin forms a complex with a related protein, XIAP, and it is this interaction that cooperatively inhibits apoptosis, and enhances tumor growth, in vivo. In unraveling this pathway, we found that a survivin-XIAP complex is not only competent to counteract cell death, but also activates a broad gene expression program in tumor cells, with upregulation of a distinct class of adhesion molecules, especially fibronectin. This has profound implications, as survivin-expressing cells become highly invasive, in vitro, and exhibit aggressive metastatic dissemination in xenograft and transgenic models, in vivo. Therefore, a unifying hypothesis that survivin functions as a novel metastasis gene, in vivo, via de novo upregulation of gene expression can be formulated, and will constitute the focus of the next cycle of CA788810. Experiments in the first specific aim will dissect the phenotypic requirements of tumor cell invasion mediated by survivin, with respect to modulation of epithelial-mesenchymal transition, matrix metalloproteinase expression, and activation of a pivotal regulator of this pathway, the Src kinase. The second specific aim will attain a comprehensive characterization of how a survivin-XIAP complex influences molecular mechanisms of gene expression. These studies will focus on the cellular and signaling requirements of fibronectin gene regulation, and elucidate their involvement in tumor cell invasion. Lastly, in the third specific aim, we will test the relevance of this pathway in metastasis models, in vivo. This will be accomplished by systematically targeting the assembly of a survivin-XIAP complex, its requirements for gene expression, and its downstream signaling effectors in xenograft studies, and in a transgenic mouse model of localized and disseminated breast cancer. Overall, these studies will unravel the molecular underpinnings of a novel pathway of tumor cell invasion at the crossroads between intracellular signaling by apoptosis regulators and modulation of adhesion molecule gene expression. The results may help in the design of novel molecularly- directed therapies that interfere with metastatic disease, an incurable and invariably fatal occurrence of cancer progression in humans.